This application is based on the applications No. 2000-053997 and No. 2000-130989 filed in Japan, the content of which is incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an arrangement to control variance of voltage and unwanted radiation noises in a wiring board, on which a semiconductor device, such as an IC, an LSI, and a transistor, is mounted, and more particularly to a wiring board, on which a digital circuit is mounted.
A wiring board of the present invention is applicable to a semiconductor device encapsuling package for sealing a semiconductor device mounted on the surface of a wiring board airtight, a hybrid integrated wiring board, on which various electronic components including a capacitor and a resistor are mounted besides the semiconductor device, etc.
2. Description of the Related Art
In a wiring board forming a predetermined electronic circuit by having thereon mounted an electronic component, such as an IC, an LSI, and a transistor, a high frequency current is generated and flows between a power source terminal and a ground terminal during the operation of the electronic component. The high frequency current propagates across the electronic circuit, which triggers a malfunction of the circuit itself or causes unwanted radiation noises to be generated.
In particular, noticeable high frequency noises are generated at the power source and ground in the vicinity of a circuit that operates digitally, and when these noises propagate to the power source and ground in an area where a connection with a cable or the like is established, common-mode currents are produced in the cable, which give rise to strong radiation noises. Also, resonance generated depending on the shapes of the power source layer and ground layer or an interlayer capacity therebetween is the principal cause of variance of potential.
As a countermeasure against such inconveniences, a method is employed, in which the high frequency current is trapped by mounting a decoupling capacitor in the vicinity of the electronic component that becomes a noise source.
Also, Japanese Laid-open Patent Application No.9-266361 proposes to reduce the high frequency electromagnetic wave propagated to the power source layer and ground layer in the wiring board at the end of the board by interposing a capacitor between the power source layer and ground layer and surrounding the outer circumference of the board entirely with the capacitor.
However, the above method of using the decoupling capacitor can trap only the high frequency current at a particular frequency that is determined by a capacity and parasitic inductance of the decoupling capacitor, and has an adverse effect that another noise-causing high frequency current is produced at the other frequencies. Using a plurality of capacitors each having a different capacity is proposed as a solution of this problem. Nevertheless, it is still difficult to provide an improvement over a broad range of frequencies.
Also, the method of providing the capacitor to the outer circumference of the board entirely demands a capacitor of a specific shape and a great number of chip capacitors. This poses a problem that the cost is increased by the capacitor or the productivity is reduced by the time and labor required to attach the capacitor.
On the other hand, a CPU and an LSI are improved to operate at a higher frequency to increase a processing rate in the information communication field, and there has been an increasing need for a preventive measure against noises in a high frequency band of a millimeter frequency band or a microwave frequency band. However, the above-described conventional noise removing methods are not satisfactory in practical use.
It is therefore an object of the present invention to provide a wiring board capable readily controlling variance of power source voltage and unwanted irradiation noises developed across a power source layer and a ground layer over a broad range of frequencies with a simple arrangement.
Another object of the present invention is to provide a wiring board capable readily controlling variance of power source voltage in a frequency band of GHz and unwanted irradiation noises developed across a power source layer and a ground layer over a broad range of frequencies with a simple arrangement.
Still another object of the present invention is to provide a wiring board capable readily controlling unwanted irradiation noises over a broad range of frequencies with a simple arrangement by preventing variance of power source voltage developed across a power source layer and a ground layer connected to a digitally operating electronic component from propagating to another power source layer and another ground layer, to which an input/output terminal, a cable, or the like is connected.
(1) A wiring board of the present invention, on which an electronic component is mounted, comprises: a dielectric substrate; a wiring circuit layer formed on a main surface and/or a back surface of said dielectric substrate; a power source layer formed on a main surface and/or a back surface of said dielectric substrate, and/or within said dielectric substrate; a ground layer formed on the main surface and/or back surface of said dielectric substrate, and/or within said dielectric substrate; and a connector for electrically connecting said electronic component and power source layer, and said electronic component and ground layer, and is characterized in that: either or both of said power source layer and ground layer have a low resistance area having a low sheet resistance, and a high resistance area having a high sheet resistance; said high resistance area is provided at a circumference of said low resistance area; and said connector is connected to said low resistance area.
According to the above wiring board, by providing the high resistance area at the periphery of the power source layer and/or ground layer, noises caused by a high frequency current produced in an electronic component composed of an IC or an LSI can be attenuated or dispersed in the high resistance area. Hence, resonance caused by high frequency noises does not occur between the power source layer and ground layer, and therefore, it is possible to control variance of voltage across the power source layer and ground layer while reducing irradiation noises, thereby ensuring reliability of the circuit.
(2) A wiring board of the present invention, on which an electronic component is mounted, comprises: a dielectric substrate; a wiring circuit layer formed on a main surface and/or a back surface of said dielectric substrate; a power source layer formed on a main surface and/or a back surface of said dielectric substrate, and/or within said dielectric substrate; a ground layer formed on the main surface and/or back surface of said dielectric substrate, and/or within said dielectric substrate; and a connector for electrically connecting said electronic component and power source layer, and said electronic component and ground layer, and is characterized in that: either or both of said power source layer and ground layer have a high conductivity area having a high conductivity, and a low conductivity area having a low conductivity; said low conductivity area is provided at a circumference of said high conductivity area; and said connector is connected to said high conductivity area.
According to the above wiring board, by providing the low conductivity area at the periphery of the power source layer and/or ground layer, noises caused by a high frequency current produced in an electronic component, such as an IC and an LSI, can be attenuated or dispersed in the low conductivity area. Hence, resonance caused by high frequency noises does not occur between the power source layer and ground layer, and therefore, it is possible to control variance of voltage across the power source layer and ground layer while reducing irradiation noises, thereby ensuring reliability of the circuit. The present invention is remarkably effective in preventing noises on a high frequency current in a high frequency band of 1 GHz or over, in particular, the millimeter frequency band or microwave frequency band of 10 GHz or over, generated in the electronic component, such as an IC and an LSI.
When a roughness on the interface between the low conductivity area and dielectric substrate is two or more times as great as a skin depth at the highest frequency of a signal transmitted to the wiring board, in particular, a resistance to a high frequency current passing along the surfaces of the power source layer and ground layer increases, which makes it possible to attenuate the high frequency noises effectively.
(3) A wiring board of the present invention, which an electronic component is mounted, comprises: a dielectric substrate; a wiring circuit layer formed on a main surface and/or a back surface of said dielectric substrate; a power source layer formed on a main surface and/or a back surface of said dielectric substrate, and/or within said dielectric substrate; a ground layer formed on the main surface and/or back surface of said dielectric substrate, and/or within said dielectric substrate; and a connector for electrically connecting said electronic component and power source layer, and said electronic component and ground layer, and is characterized in that: either or both of said power source layer and ground layer are separated into a first area and a second area by a high impedance strip; and said first area includes a connection to said connector.
According to the above wiring board, by separating the power source layer and/or ground layer connected to an electronic component, such as a digital IC or an LSI, into the first area including the connected portion to that electronic component and the second area of the rest by the high impedance strip, high frequency noises generated in the electronic component can be trapped and reduced in the high impedance strip. Consequently, it is possible to control variance of potential of the power source layer and ground layer in the second area.
Connecting an input/output terminal or the like to the second area can reduce irradiation noises from the input/output terminal, a cable or the like. In addition, high frequency noises caused by resonance in the power source layer and ground layer are attenuated or dispersed in the high impedance strip, and therefore, it is possible to lessen variance of voltage across the power source layer and ground layer, thereby ensuring reliability of the circuit.
The present invention is particularly effective when the electronic component operates digitally.
The following description will describe in detail a concrete arrangement of a wiring board of the present invention with reference to the accompanying drawings.